After taxiing and holding behind a Cessna Citation, the pilots of the Airbus A320 operated by Vueling complained of an unpleasant smell and irritations. During the initial climb, they experienced some physical disorders leading to a partial incapacitation. Given this partial incapacitation, the crew asked a cabin crew member to monitor them and donned oxygen masks which allowed them to divert and land without further incident.
Despite the wide range of actions undertaken, the investigation was not able to factually identify what caused the flight crew’s symptoms and physical discomfort. The hypothesis of them having inhaled an excessive quantity of carbon monoxide, contained in exhaust gases emanating from the Cessna Citation which had been in front of the A320, is consistent with the information collected and can explain the symptoms observed (dizziness and nausea). Nitrogen oxide and sulphur oxide compounds present in exhaust gases may also have contributed to the acrid and irritating odours smelt while taxiing. However, it cannot be excluded that the crew were intoxicated by another substance which either quickly disappeared or which was not specifically searched for in the samples taken from the aeroplane as to date, not identified, even in the most recent studies.